The present invention relates to an apparatus and a process for biological wastewater purification. In particular, the present invention relates to an apparatus and a process for biological wastewater purification in which, in an activation tank, at least one lamellae pack for separating off biologically active bacterial cultures which are suspended in the wastewater is provided, and a forced circulation apparatus which is disposed in the bottom region of the activation tank.
In the prior art it is known per se to provide, for purifying wastewater, activation tanks in which wastewater pollutants are degraded, with supply of oxygen, by biologically active bacterial cultures or microorganisms suspended in the water. It is also known to provide secondary sedimentation tanks in which the biologically active bacterial cultures are separated from the water by sedimentation, the resultant sludge then being pumped back to the activation tank. In the prior art, activation tanks and secondary sedimentation tanks are thus to be considered as an operational unit, since the activation tank and the secondary sedimentation tank form a circuit in which the bacterial density, measured as dry matter content, in the activation tank is a function of the sedimentation action in the secondary sedimentation tank.
Furthermore, in the prior art, for the separation or sedimentation in the secondary sedimentation tank, the use of lamellae separators has been proposed, which employ lamellae packs which consist of a multiplicity of lamellae. The wastewater is passed over these lamellae packs in the secondary sedimentation tank, which, owing to the considerable surface area of the lamellae, leads to the desired separation of the bacterial cultures as sludge.
It is important in this case to differentiate two fundamentally different types of activation tank. Firstly there are the circulation ditches in which the mixed liquor is circulated, and there are sequential-flow tanks in which both the activation tank and the secondary sedimentation tank are connected in series and flow passes through thee sequentially
DE-A 43 29 239 discloses a process and an apparatus for biological wastewater purification in which the bacterial content in the activation tank is increased by lamellae packs which are disposed at the flow-path end of the activation tank at a distance from the outlet of the same. Providing the lamellae packs in the activation tank is said to have the advantage that recycling the sedimented bacterial sludge in a separate return sludge stream becomes unnecessary, which avoids destruction of the flock structure via the circulation pumps used. In addition, blockage of the lamellae by sludge deposits or the like is said to be avoided.
Compared with this prior art, the present invention is based on the inventive observation that the described process and the corresponding apparatus according to the above prior art are unusable industrially. Experiments have found that mounting the lamellae pack at the end of the sequential-flow tank described in the prior art leads to the bacterial sludge which has been separated in or on the lamellae collecting below the lamellae and tailing back into the lamellae pack, from where it is entrained by the wastewater stream towards the secondary sedimentation tank. In the limiting case this leads to the total breakdown of the system.
The present invention thus faces the problem of providing an apparatus and a process for biological wastewater purification which function industrially with high reliability and lead to the desired increase in bacterial content in the activation stage. As a result it becomes possible to avoid capital costs for installing additional tanks for ensuring the required purification performance.
The problem underlying the invention is solved by an apparatus and process for biological wastewater purification according to the present invention.
In detail, the inventive solution according to the present invention is based on providing forced circulation of degradation means in the bottom region of the activation tank below the lamellae pack used. As a result of the wastewater to be purified flowing over the lamellae pack, the degradation means (bacterial cultures or microorganisms) suspended in the wastewater are separated off by sedimentation and fall as thickened degradation means sludge to the bottom region of the activation tank. In the bottom region is provided the forced recycling of degradation means according to the invention which takes up the thickened separated degradation means sludge and recycles it back to the activation tank. By means of the bacteria/microorganism content Increased in this manner in the activation stage, an enhanced performance based on the available reaction space can be achieved.
According to the preferred embodiment of the present invention, there is provided additionally to the activation tank a secondary sedimentation tank in which degradation means remaining in the wastewater are separated off by sedimentation. The resultant thickened degradation means sludge is then recirculated to the activation tank via a return. The double recirculation of the degradation means provided in this manner, once from the end region of the activation tank, and from the secondary sedimentation tank, permits a highly precise setting of the bacterial or microorganism content in the activation tank by using a suitable control circuit.
According to the preferred embodiment of the present invention, the inventive forced recirculation of degradation means consists, firstly, of a transport means, for example a pump or a siphon, and secondly a bottom scraper (for example a Zickert(trademark) scraper or other hydraulically driven sludge scraper). This inventive configuration of the forced recirculation of the degradation means permits, in a particularly efficient manner, firstly collection of the degradation means sludge which is collected in the bottom region of the activation tank below the lamellae, and secondly efficient removal of the collected sludge back to the activation tank.
According to the preferred embodiment of the present invention, the bottom region below the inventive lamellae pack is inclined in relation to the water surface for the forced recirculation of degradation means. The inclination of the bottom region, together with the preferably used bottom scraper permits a particularly efficient collection of the degradation means sludge in the region of the inventively used transport means.
In the preferred embodiment of the present invention, the inventive at least one lamellae pack is disposed at the flow path end in the activation tank, with, in addition, partition over which wastewater flows being provided, which partition prevents direct action of wastewater flow on the at least one lamellae pack. This prevents the flowing wastewater from undesirably making the process of deposition of the bacterial or microorganism cultures on the lamellae turbulent.
Preferred embodiments of the present invention describe two different disposition possibilities of the inventive lamellae pack. In the ~ particularly preferred embodiment of the present invention, the lamellae are disposed in parallel to the direction of the wastewater flow. In combination with the partition over which wastewater flows this permits a particularly laminar and controlled wastewater stream which suits the efficient separation in the activation tank.
Further preferred embodiments result from the subclaims which are not discussed here in detail.